EDIT: Haha, skimmed through this posts a little after I posted it. It's pretty poorly written, doesn't answer your questions, and I have no idea what I was thinking. It was more of a 6-in-the-morning lull than anything else. I'll try to help later.
If you open your own sharing network (say you start Demonoid2.com), you're going to cull a lot of attention. I like writing about legal issues so I will stray far away from the focus and begin rambling.
There are actually various legal retentions that allow you to indulge in open p2p file distribution. The only trouble is that (a) nobody really knows how well they will stand up in court and (b) nobody wants to spend the money to see.
However, bear in mind that legally, you can share whatever you want as long as those in your sharing capacity and network comply to all copyright protection laws. This can be as simple as making someone check a compliancy box when they register for your tracking aggregator.
Now you can claim that all distribution is conducted under copyright law. The reason you can still share is because those who are downloading the information can simply claim that they already own the original file (movie, game, app) and are seeking a backup of it. This DOES stand up in court.
So now you have a sharing network of "people that already own the shit you're distributing" (yeah, right).
If any bullshit bureau comes after you, tell them you're opting to counter-claim if they even point a finger at you. Explain that your network is built on a complaincy that accepts and agrees to all copyright laws. This isn't so the bureau goes "oh, I guess he does have a legal sharing network. they probably are just backing up their dvd movie collections." It's so they know that you know the exact law they are trying to wring you for. Make sure you threaten a counter-claim for the forgone time, income, etc. that you will spend defending yourself in court. Make sure they know you are going to defend yourself. Legal entities [that deal with internet law] are fucking scared of people that defend themselves because lawyers are will pretend to put up a fight and then quit, and lawyers don't know shit about interweb legality. Law school is FIVE YEARS behind cutting edge legal press. If you defend yourself, you make yourself a wildcard.
If the bureau finally goes through with it and brings you into court, if you can "ride the law" and explain that you are operating at 100% compliancy with any laws that apply to you, you will win. Legislation may pass after you win that changes the laws so you can't win again, but you will win round 1.
This is how anyone that's ever pioneered anything on the internet has stayed in business or won their first legal battle. Napster is the best example of a faggot that didn't know what to do and sent in a shitfuck lawyer. This is the reason Kazaa, Morpheus, BearShare, etc. (All American legal-based) could spring up while Napster was getting wide coverage for being a piracy network.
So, make uses agree to copyright compliancy. You don't need a login system. Just make a popup box that makes them click Agree before they can peer your tracker.
NEXT
How does RapidShare and other datashare models operate legally?
First, these guys fly under the radar because they don't get the piracy publicity p2p and torrents do.
But if they were ever taken to court for piracy, they could say this: "We are based on anonymity and do not stake responsibility for the conduct of our anonymous userbase." Currently, you can claim that you are an anonymous network under law and waiver responsibility. There's more to it than that, but there's the gist of it. RapidShare can simply say that they do not endorse the distribution of pirateware, and it's illegal for the government to shut down such a service because of anonymous user conduct. That's like closing down Target for lewd behavior because someone spraypainted a giant cock on the wall.
Holy shit it's late and I'm tired of typing. I started talking about legal self-defense there for a little (a little too long-sighted for your questions), but I can help you cater to the legal side of things so you wont get in trouble.
Remember that internet law is the newest thing on the block. Nobody knows how to interpret the shit legislation and it's in need of some serious rewording. However, that doesn't happen until people have the balls to use the shitty wording to defend their ass. Legislation is rewritten after someone wins a case they shouldn't have. It's our law-system's way of working out the kinks.
You hear about torrent sites closing left and right. You don't hear them even trying to make a stand in court. Instead the owners don't know how to defend themselves and then make the mistake of getting some lawyer who thinks he know internet law because he won a domainsquatting case in '99.
I'll bring some better answers to the table "tomorrow." It's like 6am.
